1. Field of the Invention
The present invention relates to a jig for adjusting curvature of a substrate, and more particularly, to a jig for adjusting curvature of a substrate, in which curvature of the substrate in a cassette used in fabrication of a liquid crystal display (LCD) device is measured, for easy fabrication of the cassette.
2. Background of the Related Art
Applications of the LCDs have been diversified from watches, calculators, PC monitors, and notebook computers to TVs, monitors for aviation, PDAs (Personal Digital Assistants), and mobile stations owing to features of low voltage operation, low power consumption, realization of full colors, light weight, thin, and compact.
The LCD is provided with a liquid crystal display panel for displaying a picture, and a circuit part for driving the liquid crystal display panel.
The LCD panel has a first substrate having thin film transistor (TFT) array formed thereon, a second substrate having color filter array formed thereon, and a liquid crystal layer formed between the two substrates.
The first glass substrate having the TFT array formed thereon is provided with a plurality of gate lines arranged in one direction at fixed intervals, a plurality of data lines arranged in a direction perpendicular to the gate lines at fixed intervals to define pixel regions, a plurality of pixel electrodes in respective pixel regions for displaying a picture, and a plurality of thin film transistors in respective pixel regions at cross points of the gate lines and the data lines for being turned on/off in response to driving signals on the gate lines for transmitting a picture signal from the data lines to the pixel electrodes.
The second glass substrate having the color filter array formed thereon is provided with a black matrix layer for shielding a light from parts excluding the pixel regions, a R, G, B color filter layer formed opposite to the pixel regions for realizing colors, and a common electrode formed on an entire surface inclusive of the color filter layer. Of course, the common electrode is formed on the first substrate in an LCD of an IPS mode.
The first and second substrates are bonded together, with a space between the two substrates, and a liquid crystal layer is formed between the first and second substrates.
The substrate is a glass plate of which weight portion in the LCD panel is great. Therefore, in order to reduce weight of the LCD panel, it is required to reduce weight of the glass substrates, at the end, to require thin glass substrates.
A process for fabricating the LCD may be divided into three processes of a substrate fabrication process, a cell fabrication process, and a module fabrication process.
The substrate fabrication process may be divided into processes of fabrication of the TFT, and the color filter on the cleaned glass substrates. The TFT fabrication process is a process for fabricating a plurality of thin film transistors and pixel electrodes on a first substrate, and the color filter fabrication process is a process for forming R, G, B color filter layer by using dye or pigment on a second substrate having a light shielding layer formed thereon, and the common electrode (ITO).
The cell fabrication process is a process for fabricating cells of the LCD by scattering spacers between two substrates of the first substrate having the TFT fabrication process finished, and the second substrate having the color filter fabrication process finished, bonding the two substrates, and injecting liquid crystal between the two substrates, and, finally, the module fabrication process is a process for fabricating a circuit part for processing signals, and connecting the LCD panel and the signal processing circuit part, to fabricate a module.
In the LCD fabrication process, it is required that the substrates are conveyed or carried to an apparatus required for a process, progressively, or in a form of group, for passing through the substrate fabrication process, the cell fabrication process, and the module fabrication process. Moreover, since entire fabrication line can not be stopped for repair of a part of the fabrication apparatus in view of the fabrication process, it is required that the fabrication apparatus is provided with a means for temporary storage of the substrates.
To meet this requirement, a cassette is used. By moving the cassette with a plurality of the substrates stored therein, the plurality of substrates are movable at a time. Though dependent on the cassettes, when the plurality of substrates are stored in the cassette, the substrates are bend.
Such a cassette will be explained, with reference to the attached drawings. FIG. 1 illustrates a front view of the cassette.
Referring to FIG. 1, the cassette has hexahedral body 13 for storing the plurality of substrates in horizontal position. There are vertical frames 13a vertical to ground at at least opposite two surfaces of the body 13, a plurality of slots 15 for supporting edges of the substrate 11, and stoppers 17 at opposite side of a substrate entrance for stopping the substrate 11 inserted into the cassette.
The vertical frame 13a having the slots 15 formed thereon may be formed, not only at the four sides of the hexahedral body, but also at corners of the cassette, more. The slots 15, around 20 in number on each of the vertical frame 13a, have a fixed length and width, for supporting edges, or sides, of the substrates 11.
As explained, the substrate is a thin glass plate for reducing weight of the LCD, which is liable to bend. Therefore, the length of the slot 15 is a major factor of fixing curvature of the substrate 11, the shorter the slot 15, the greater the curvature of the substrate 11, and the longer the slot 15, the smaller the curvature of the substrate 11.
That is, FIG. 2 illustrates sag of the substrate schematically, wherein the substrate 11 is supported on the slots 15, which are fixed to the vertical frames 13a. 
A depth Y of the sag of the substrate 11 can be measured with a height gage, and since a robot is to bring the substrate 11 into the cassette and place on the slot 15, for not giving interference to the movement of the robot, it is required that the depth Y of sag is kept to be within a certain value for preventing the substrates from overlapping with the other due to the sag.
After all, the longer the length of the slot 15, the smaller the depth of the sag Y as the substrate 11 is supported on the slots 15 the more, and the shorter the length of the slot 15, the greater the depth of the sag Y as the substrate 11 is supported on the slots 15 the less.
Therefore, it is required that the cassette is fabricated, not only to fit a size of the substrate 11, but also to have a proper length of the slot 15 depending on the curvature of the substrate.
However, the related art cassette has the following problem.
Since the slots in the cassette is fixed to the vertical frame, it is required to fabricate a mock up of the cassette according to the curvature of the substrate, and test the mock up cassette for a plurality of time before the cassette is fabricated.
That is, for finding a slot suitable to the substrate, a plurality of fabrication of the mock up cassette is required for coping with slot length variation with a thickness of the substrate, which increases cost and requires longer production time, that drops the productivity.